Glucocorticoid-induced CREB activation and myostatin expression in C2C12 myotubes involves phosphodiesterase-3/4 signaling

• Authors: Yang Xie, Emory University; Ben D. Perry, Emory University; Daniel Espinoza, Atlanta Veterans Affairs Medical Center; Peng Zhang, Emory University; Stephen Price, Emory University
• Journal Title: Biochemical and Biophysical Research Communications
• Volume: Volume 503, Number 3
• Publisher: Elsevier: 12 months | 2018-09-10, Pages 1409-1414
• Type of Work: Article | Post-print: After Peer Review
• Publisher DOI: http://doi.org/10.1016/j.bbrc.2018.07.056
• Subjects: Chemistry, Biochemistry; Biology, Molecular
• Keywords: Science & Technology; Life Sciences & Biomedicine; Biochemistry & Molecular Biology; Biophysics; Glucocorticoid; Myostatin; CREB; Skeletal muscle; Gene expression regulation; Insulin resistance; SKELETAL-MUSCLE ATROPHY; NUCLEAR-PROTEIN CBP; FUNCTIONAL-ANALYSIS; GENE; KINASE; TRANSCRIPTION; INSULIN; UBIQUITIN; CACHEXIA; PATHWAY

Abstract

Muscle atrophy in metabolic conditions like chronic kidney disease (CKD) and diabetes are associated with glucocorticoid production, dysfunctional insulin/Akt/FoxO3 signaling and increased myostatin expression. We recently found that CREB, a transcription factor proposed to regulate myostatin expression, is highly phosphorylated in some wasting conditions. Based on a novel Akt-PDE3/4 signaling paradigm, we hypothesized that reduced Akt signaling contributes to CREB activation and myostatin expression. C2C12 myotubes were incubated with dexamethasone (Dex), an atrophy-inducing synthetic glucocorticoid. Akt/CREB signaling and myostatin expression were evaluated by immunoblot and qPCR analyses. Inhibitors of Akt, phosphodiesterase (PDE)-3/4, and protein kinase A (PKA) signaling were used to test our hypothesis. Incubating myotubes with Dex for 3–24 h inhibited Akt phosphorylation and enhanced CREB phosphorylation as well as myostatin mRNA and protein. Inhibition of PI3K/Akt signaling with LY294002 similarly increased CREB phosphorylation. Isobutyl-methylxanthine (IBMX, a pan PDE inhibitor), milrinone (PDE3 inhibitor) and rolipram (PDE4 inhibitor) augmented CREB phosphorylation and myostatin expression. Inhibition of protein kinase A by PKI reverted Dex- or IBMX-induced CREB phosphorylation and myostatin expression. Our study provides evidence supporting a newly identified mechanism by which a glucocorticoid-related reduction in Akt signaling contributes to myostatin expression via CREB activation.